Amid an escalating crisis between neighboring nations, President Trump and Mexican President Enrique Peña Nieto had a “constructive” and “productive” telephone conversation early Friday.

The two presidents spoke for about an hour, according to near-identical official statements from both presidential press offices.

The conversation seemed a clear effort to tone down rising tensions a day after Mexico’s leader canceled plans to meet with Trump in Washington, D.C., next week. Peña Nieto scrapped the visit following Trump’s insistence that Mexico foot the bill to build a wall along the U.S.-Mexico border.

The two presidents “had a productive and constructive call” and “recognize their clear and very public differences” about who would pay for the proposed wall, the White House said.

Both leaders “agreed to work these differences out as part of a comprehensive discussion on all aspects of the bilateral relationship,” it said.

One of America’s most important strategic relationships plunged to a new low Thursday when an escalating dispute over a proposed wall on the U.S.-Mexico border prompted Mexican President Enrique Peña Nieto to cancel a planned visit to the White House.

President Trump has been in office barely a...

(Kate Linthicum and Tracy Wilkinson)

The two chief executives also agreed for now “not to speak publicly about this controversial theme,” said the statement from the Mexican president’s office, apparently alluding to the dispute about payment for the wall. The White House statement did not mention any agreement to limit public discussions.

Trump’s signature proposal, which would add to the 653 miles of fencing and barriers already along the 2,000-mile border, has sparked outrage in Mexico.

The government there has repeatedly rejected Trump’s insistence that Mexico would pay for it. Many Mexican commentators and average citizens view the suggestion as a humiliation.

The two nations, which share not only a long frontier but also considerable history and culture, historically have cooperated on a range of issues. Decades of good relations appear to have deteriorated rapidly in recent days, however.

Themes discussed in Friday’s call, the White House said, included the U.S. trade deficit with Mexico — a major concern of the Trump administration — and “the importance of the friendship between the two nations, and the need for the two nations to work together to stop drug cartels, drug trafficking and illegal guns and arms sales.”

Mexican officials highlighted their cooperation with U.S. authorities on drug trafficking and the flow of Central Americans to the United States through Mexico. The smuggling of arms from the U.S. to Mexico is another issue they have raised.

Trump has also sent tremors through the Mexican economy by vowing to renegotiate the North American Free Trade Agreement — involving the United States, Mexico and Canada — and tax imports to the United States.

During the presidential campaign, he regularly assailed U.S. manufacturers who have set up shop in Mexico to take advantage of cheap labor and a liberal trade regimen. Mexico’s economy is heavily dependent on exports to the United States, which accounts for almost 80% of Mexico’s export market.

Mexicans have been riveted by the rift between Peña Nieto and Trump, and on Friday, the country’s wealthiest businessman weighed in on the situation during a rare news conference.

Carlos Slim, a telecommunications tycoon and the third-richest person in the world, held up a copy of one of Trump’s books, “Crippled America: How to Make America Great Again,” and said the new U.S. president should be expected to follow through on his campaign promises — and threats.

“There are no surprises with him” said Slim, who criticized Trump during the election campaign but had dinner with him shortly after Trump’s victory. He said the two had not spoken since the dinner.

Slim called Trump’s protectionist economic policies an “attempt to return to the past” and said an import tax would hurt business interests and American consumers more than it would hurt Mexico.

The billionaire said he was pleased that Trump and Peña Nieto had spoken by phone, and called on Mexicans to unite behind their president as negotiations over NAFTA and on other issues go forward.

“What is clear is that they will not be able to negotiate on Twitter,” Slim said.